The stern tube is the tube through which the propeller shaft passes out through the stern of the ship, connecting the engine room equipment to the propeller. As the shaft rotates inside the tube, it is exposed to the high pressure of water surrounding the ship. Hence, the bearing and sealing arrangement of the shaft inside the tube is of great importance for the operation and maintenance of the ship.
In order to ensure smooth functioning and reduce the wear and tear of the shaft surface in contact with the bearings/seals, a chrome liner is provided on the surface area of the shaft. The present work focuses on studying the concept, installation location and importance of a chrome liner on the ship’s stern tube.
A chrome liner is a sleeve or lined surface on a propeller shaft over which a harder material such as chrome is deposited as a facing. It is not the shaft itself, but rather the shaft liner or shaft carrying such a facing at the critical wearing surface.
Key properties of chrome plating include:
The exact coating thickness and specification always depends on the manufacturer and shaft design, so these values should be taken from the relevant maker’s manual rather than assumed.
The chrome liner is generally fitted at the shaft liner or on the shaft surface exactly at the point where it passes through the stern tube seals or bearings. In many designs, the propeller shaft is protected by a separate shaft liner (often bronze or similar material) and the chrome coating may be applied over this liner surface or directly on the shaft area contacting the seal.
As the propeller shaft rotates, the seal rings (or bearing surface) remain in constant contact with the chrome coated surface. Because chrome is extremely hard and smooth:
During routine inspection or shaft withdrawal engineers should check:
The chrome liner may be a small part of the overall stern tube system but it plays a big role in keeping the shaft sealing arrangement reliable. By providing a hard, smooth and corrosion resistant running surface, it helps reduce wear, minimizes leakage risk and extends the service life of expensive shaft components.
It provides a hard, smooth, wear resistant surface for the seal or bearing to run against.
Because of its high hardness, smooth finish and good corrosion resistance.
At the shaft or shaft liner surface, where it contacts the stern tube seals or bearing.
It can cause increased wear, poor sealing and possible water leakage into the stern tube.
By checking for scoring, pitting, wear and comparing dimensions against manufacturer limits.
A shaft liner is the protective sleeve fitted on the shaft, while the chrome liner refers to the hard chrome coating applied on that surface for wear protection.
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